I think there is a general misconception that if a language is not new and growing, then it is somehow going away. If anything, it's probably the opposite. Something like inertia is a much better predictor for language lifetime than than growth or features. In practice, the longer a language has been around and the more likely it is to stick around.
I think this is called the Lindy effect: https://en.wikipedia.org/wiki/Lindy_effect
> The Lindy effect is a theorized phenomenon by which the future life expectancy of some non-perishable things, like a technology or an idea, is proportional to their current age. Thus, the Lindy effect proposes the longer a period something has survived to exist or be used in the present, the longer its remaining life expectancy.
As someone who doesn't write Ruby, even I can grok RoR in a few hours. And even though it's boring and not trendy, it gets the job done for a lot of use cases.